Answer/Step-by-step Explanation:
1. 3x - 10 +4 if x = 3
To evaluate, plug in the value of x in the expression given
3(3) - 10 + 4 = 9 - 10 + 4
= 3
2. 
if x = -12
- 6 - 72 = - 78
3. 8(x - y), if x = 2, y = 6
8(2 - 6) = 8(-4) = -32
4. x + xy, if x = 3, y = -2.5
3 + (3)(-2.5) = 3 + (-7.5)
= 3 - 7.5 = - 4.5
5. (2x)² + 6, if x = -2
(2*-2)² + 6 = (-4)² + 6
= 16 + 6 = 22
6. 3x + 4y - 3x, if x = 2, y = 4
3(2) + 4(4) - 3(2) = 6 + 16 - 6
= 16
7. 
If x = -2
20 + (-2) = 20 - 2 = 18
8. 3(8x - 10) + 5x, if x = ½
3(8*½ - 10) + 5(½)
3(4 - 10) + 2.5
3(-6) + 2.5 = -18+2.5 = - 20.5 or 20½
9. x + 8y - (x)², if x = -5, y = ¼
-5 + 8(¼) - (-5)² = -5 + 2 - (25)
= -3 - 25 = -28
10. (8x)² + 6x + 2, if x = -3
(8*-3)² + 6(-3) + 2 = (-24)² - 18 + 2
= 576 - 18 + 2 = 560
11. 2x² + 4y² + xy, if x = ½, y = 2
2(½)² + 4(2)² + (½)(2)
= 2(¼) + 4(4) + 1
= ½ + 16 + 1 = ½ + 17 = 17½
12. 8x + 2y, if x = 1.5, y = -2.2
8(1.5) + 2(-2.2)
12 - 4.4 = 7.6
13. 
if x = 8.
= 5 + 4 = 9
14. 3x - 8x² + 7, if x = 4.5
3(4.5) - 8(4.5)² + 7
13.5 - 8(20.25) + 7
13.5 - 162 + 7 = -141.5
15. -2x² + 8y, if x = 3, y = -9
-2(3)² + 8(-9)
-2(9) - 72 = - 18 - 72 = 90
16. (-5x)² - 3x + x, if x = -3.5
(-5*-3.5)² - 3(-3.5) +(-3.5)
(17.5)² + 10.5 - 3.5
306.25 + 10.5 - 3.5 = 313.25
